She has her trainer to thank for her fit physique, and shared how she put in a lot of hard work and some major discipline to get her body back.

"Shout out to my trainer @fitgurlmel who really changed my body," the 37-year-old reality star wrote alongside a bikini selfie that showcased her taught tummy. "When I wasn’t happy with what I saw back in the mirror, I spent a whole year training so hard -- five or six days a week -- putting in a lot of work and changed the way that I [ate]."

Kim added that while the workouts were "crazy" and she despised doing sprints, she feels "so much more confident" these days with how she looks.

"There’s such a noticeable difference," she continued. "I am firm and less cellulite and so much more confident. SO THANK YOU for waking up at 5 a.m. to do crazy body building workouts and sprints that I hate and putting me on to this lifestyle."

Kim -- who was recently vacationing in Turks & Caicos with her sister, Kourtney Kardashian -- posted several additional selfies, including one in which she is lounging on the beach while protecting her face from the sun with a "Calabasas" ball cap.

"Calabasas girl in Turks," she wrote, referencing the city she lives in just outside of Los Angeles with husband Kanye West and their three children, 4-year-old North West, 2-year-old Saint West and 3-month-old Chicago West.

Other selfies included Kim posing in a mirror wearing a hot-pink bikini, a snapshot of her sitting on a paddle board in a fiery orange swimsuit, and one in which she is sitting back-to-back on the beach with Kourtney.